1. Field of the Invention
The present invention relates to an image forming apparatus such as a copier, printer, and the like using an electrophotographic system or a static recording system.
2. Related Background Art
In the image forming apparatus using an electrophotographic system, for example, a static latent image is formed on a surface of a photosensitive drum or a photosensitive belt, which is an image bearer, and the static image on the image bearer is developed by a developer, such as toner, to visualize an image as a toner image. The developed image is transferred to a transferring material by a transferring apparatus, to cause the toner image to be borne by the transferring material, and the toner image is fixed to the transferring material by heating and pressing by a fixing apparatus. By sequentially carrying out these steps, the image is formed.
Meanwhile, toner is consumed as the image forming apparatus is used and hence, a user should supply toner. Known methods for supplying toner include charging only toner in the image forming apparatus, replacing the developing apparatus including a toner container, or replacing a unit including the photosensitive drum.
There are methods for detecting of the amount of unused toner to inform the user of the time to replace toner. Conventional methods for residual toner detection are as follows.
In developing the static latent image formed on the image bearer by powder toner, toner is adsorbed and transferred by a static force. Toner is previously magnetized and then an electrostatic force is applied to the developing roller in the developing apparatus caused by a voltage difference to cause the toner to be adsorbed to the surface of the developing roller. The developing roller is disposed opposite to the image bearer and an electrostatic force stronger than that of the developing roller is applied to the image bearer. Then, toner is transferred and adsorbed from the developing roller to the image bearer and the latent image on the image bearer is visualized by toner.
Thus, the method for detecting a residual toner amount employs the voltage to be applied to the developing roller. Voltage is applied to the developing roller in order to adsorb and transfer toner as described above and the voltage and the electrostatic force are effective to all radial directions of the developing roller. For example, when an antenna, which is made of a conductive material is disposed in a position distant from the developing roller, an electric charge is generated in the antenna side by an electric potential difference. Hence, if toner which is a dielectric material exists between the developing roller and the antenna, the electric charge changes compared with absence of toner. As the amount of toner differs, the magnitude of the electric charge also differs and thus, the residual amount of toner can be detected by measuring the electric potential according to the electric charge to know relative comparison with the amount of toner.
However, there are problems in the conventional residual toner detection method as follows.
As shown in FIG. 4, the antenna 30 for measurement of the electric charge is disposed in the toner container 31 and thus, disturbs replacement of the toner container 31 (or, the developing apparatus or a process cartridge) for toner supply. In FIG. 4, a reference numeral 6 denotes a drum unit having a photosensitive drum 1.
In addition, as shown in FIG. 5, a contact 34 of antenna side in the toner container 31 should be attached to and detached from a contact 35 of main body side of the image forming apparatus. However, the conventional residual toner detection method is the detection method by measuring a micro voltage and therefore, a low reliability of the contact point does not allow for detection of a correct residual toner amount. Particularly, in a color image forming apparatus, as shown in FIG. 6, having a plurality of developing apparatus 4BK, 4Y, 4M, and 4C, antennas 30BK, 30Y, 30M, and 30C are disposed in developing apparatus 4BK, 4Y, 4M, and 4C, respectively, and hence, the increased number of the contact points results in lower reliability of the image forming apparatus and also a plurality of 30BK, 30Y, 30M, and 30C are necessary and hence, the cost increases. For information, in FIG. 6, the reference numeral 6 denotes a photosensitive drum unit having a photosensitive drum 1.
An object of the present invention is to provide an image forming apparatus of high reliability of the contact point for detecting an amount of the developer.
Another object of the present invention is to provide an image forming apparatus comprising: an image bearer for bearing a static image; an exchangeable type developing for developer the static image on the image bearer, the developing apparatus comprising, a developing chamber having a developing roller in an opening opposite to the image bearer, and a containing chamber for containing a developer to be supplied to the developing chamber; a detection electrode disposed outside the developing apparatus and in which a voltage is induced; and detection means for detecting an amount of the developer in the containing chamber on the basis of an induced voltage of the detection electrode.
Further objects of the present invention will be apparent from the following description.